Republican presidential candidate Herman Cain speaks on Capitol Hill in Washington in early November. In a rare moment of introspection Cain recently acknowledged that he thought the biggest misconception about him was that he was not serious. For an instant he seemed reflective, then he turned on the salesman's charm: "I'm Herman Cain," he said, grinning. "And I'm not running for second."

Meanwhile, the woman, Ginger White, told a local Fox news affiliate that she and Cain were involved in an extramarital affair for 13 years.

Cain apparently wanted to get ahead of the story, which he learned was going to be broadcast on Fox Monday night. In a statement, his lawyer, Lin Wood, said that Cain was under no obligations to discuss the allegations publicly.

"This is not an accusation of harassment in the workplace – this is not an accusation of an assault – which are subject matters of legitimate inquiry to a political candidate," said Mr. Wood in his statement. "Rather, this appears to be an accusation of private, alleged consensual conduct between adults – a subject matter which is not a proper subject of inquiry by the media or the public."

In an effort to stanch the decline in poll numbers, the former Godfather's Pizza CEO hasn't tried to reinvent his campaign. Instead, he's doubling down on its centerpiece: the 9-9-9 tax plan that has taken so much criticism from both Republicans and Democrats.

The latest effort to sell the plan is a six-minute long YouTube video, dubbed "9-9-9: The Movie – Slaying the Tax Monster."

The "movie" takes aim at the current tax code, calling it a "dorky, mechanical monster." The clip shows an animated visual of that monster, and makes extravagant claims about the 9-9-9 plan. It would "add $2 trillion to GDP and create 6 million jobs," it claims. "Business investment would increase by a third. Wages would go up by 10 percent. At the same time, federal revenues would go up 15 percent.”

And it takes particular pains to assuage Republicans' fears of the third "9" in the plan: the 9 percent national sales tax.

"Anyone nervous about introducing a national sales tax should realize we’re essentially paying one right now," a voiceover tells viewers. "It just isn’t visible. Once these taxes are out in the open, it incentivizes savings, and doesn’t allow tourists, imports, or even underground activity to sneak by.”

And the video notes that even with the new sales tax, consumers' "out-of-pocket costs at the store stay about the same. Maybe a little less than they were before."

The problem, of course, is that so many of those claims have been debunked by nonpartisan sources. One analysis by the Tax Policy Center last month found that the plan would raise taxes on 84 percent of US households, particularly low- and middle-income families.

While it appeals to some conservatives – and certainly to die-hard Cain supporters - for its simplicity, the tax plan doesn't seem to have convinced most Americans, and "the movie" seems unlikely to change that. Instead, it may simply be the death knell in an already faltering campaign, and another in a series of odd spots, like the infamous "smoking" ad.

But all doesn't have to be totally grim for Mr. Cain. In at least one interview, Newt Gingrich has said that a Gingrich-Cain ticket could be "a real possibility" if Mr. Gingrich wins the nomination.

Of course, that was before the latest allegations of the 13-year-long affair were made public.

And given Gingrich's own history, the pairing might not be the wisest.